Antistatic agents are often used in the continuous polymerization of olefins to avoid electrostatic charging. In the context of olefin polymerization these compounds may also be referred to as antifouling agents, activity inhibitors, productivity inhibitors or kinetic modifiers. Antistatic agents can comprise compounds which have polar functional groups such as acids, ester groups, amines, amide groups, hydroxyl or ether groups that demonstrate “antistatic” behavior. Examples of antistatic compounds are polysulfone copolymers, polymeric polyamines, polyalcohols, hydroxyesters of polyalcohols, salts of alkylarylsulfonic acids, polysiloxanes, alkoxyamines and polyglycol ethers.
Quite efficient as antistatic agents are compositions which comprise more than one antistatically acting compound. U.S. Pat. No. 3,917,466 teaches antistatic additive compositions comprising a polysulfone copolymer, a polymeric polyamine, an oil-soluble sulfonic acid and a solvent. WO 2008/107371 A2 refers to similar compositions comprising specific organic solvents with a high boiling point. The use of such compositions as antistatic agents for the polymerization of olefins is, for example, described in U.S. Pat. No. 5,026,795, WO 2002/40554, WO 2007/131646 or WO 2011/072850. However, the antistatic agents described therein often negatively impact the activity of most olefin polymerization catalysts. Their efficiency is also limited, as they can create issues regarding sheeting and lump formation because of electrostatic charging for certain products such as polyolefins with relatively high molecular weight. Moreover, many commercially used mixtures contain substances such as substituted benzenes or naphthalenes that are often not approved for food contact.
Previous attempts to utilize simple chemical compounds for avoiding or reducing electrostatic charges within the polymerization reactor have been reported. For example, EP 0 315 192 A1 teaches the use of oxygen, nitric oxide, alcohols containing up to 7 carbon atoms or ketones containing up to 7 carbon atoms, while EP 0 366 823 A1 discloses a method for reducing sheeting during polymerization of α-olefins by introducing water into a polymerization reactor in order to influence the electrostatic levels at the site of possible sheet formation. The water is added by bubbling nitrogen through a tank filled with water and the water saturated nitrogen is then introduced into the olefin feed line of the reactor. However, this method is not suitable for nitrogen-free polymerization processes.
Thus, it was the object of the present technology to overcome the disadvantages of the relevant technology area and to find a process for the polymerization of olefins in the presence of an antistatic agent which is simple to carry out, does not deteriorate the product properties of the prepared polyolefins, does not impair or even improve the activity of the catalyst, provides a good operability of the polymerization process including with regards to the formation of fines (very small polyolefin particles) and may be approved for use in food, beverage and pharmaceutical applications.